|Publication number||US7501784 B2|
|Application number||US 10/599,674|
|Publication date||Mar 10, 2009|
|Filing date||Apr 4, 2005|
|Priority date||Apr 5, 2004|
|Also published as||DE102004016738B3, US20070182357, WO2005099071A1|
|Publication number||10599674, 599674, PCT/2005/51502, PCT/EP/2005/051502, PCT/EP/2005/51502, PCT/EP/5/051502, PCT/EP/5/51502, PCT/EP2005/051502, PCT/EP2005/51502, PCT/EP2005051502, PCT/EP200551502, PCT/EP5/051502, PCT/EP5/51502, PCT/EP5051502, PCT/EP551502, US 7501784 B2, US 7501784B2, US-B2-7501784, US7501784 B2, US7501784B2|
|Original Assignee||Siemens Aktiengesellschaft|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (11), Non-Patent Citations (4), Referenced by (6), Classifications (10), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a compensation apparatus in order to compensate for bearing currents in an electrical machine, and to an electrical machine which is equipped with a compensation apparatus such as this. The present invention furthermore relates to a corresponding method for compensation for bearing currents.
Nowadays, variable-speed motors are generally fed by voltage intermediate-circuit converters. These voltage-intermediate-circuit converters for feed purposes lead to bearing currents in the bearings of the motor. These bearing currents can lead to premature failure of the bearings, depending on the design of the motor. Failure is due to groove formation on the running suhigh-frequencyaces of the bearing (vibration, noise) and/or to decomposition of the bearing grease.
Current-isolated bearings, for example bearings with ceramic insulation on the outer ring, are thus widely used in order to suppress bearing currents. Alternatively, hybrid bearings have been used, with steel rings and ceramic roller bodies in order to avoid bearing currents. However, these bearings are very expensive and are thus avoided, as far as possible. Furthermore, solutions in which the rotor is grounded by means of grounding brushes are known in order to prevent bearing currents. However, the grounding brushes are subject to wear and the contact reliability is not ensured, particularly in rugged environmental conditions. Furthermore, the Rockwell company have proposed in an “Industry White Paper” entitled “Inverter-Driven Induction Motors Shaft and Bearing Current Solutions” for a specific shield to be provided between the rotor and the stator. Furthermore, in this context, converters are also known which use specific pulse patterns to reduce the bearing currents. All of these solutions have the common feature that they are relatively expensive and complex.
The object of the present invention is thus to propose an electrical machine in which the problems relating to bearing currents are solved in a simple manner. A further aim is to specify a corresponding method.
According to the invention, this object is achieved by a compensation apparatus for compensation for bearing currents in an electrical machine having a connection device for connection to at least one winding, to the housing and to the rotor of the electrical machine, and a voltage production device for production of a compensation voltage for the rotor of the electrical machine as a function of the operating voltage which is applied to the at least one winding, of the electrical machine.
Furthermore a method is provided according to the present invention for compensation for bearing currents in an electrical machine by production of a compensation voltage for the rotor of the electrical machine as a function of an operating voltage of the electrical machine, and application of the compensation voltage to the rotor of the electrical machine.
The compensation apparatus according to the invention, which is of simple design, applies an appropriate opposing voltage to the bearing, so that the electrical voltage which is caused on the bearings by the normal operating voltage on the electrical machine is compensated for. Currents therefore no longer flow via the bearing, and the life of the electrical machine can be correspondingly increased.
The voltage production device of the compensation apparatus according to the invention preferably has a transformer whose primary winding is connected between the at least one winding and the housing of the electrical machine, and whose secondary winding is connected between the rotor and the housing of the electrical machine. The transformer represents a cost-effective passive element for provision of the compensation.
The transformer can be connected to networks, for example RC combinations, varistors, in order to adjust the compensation voltage individually for the machine.
As an alternative to the transformer, the voltage production device may have an active circuit, by means of which the compensation voltage can be produced from the operating voltage which is applied to the electrical machine. An active circuit such as this makes it possible to carry out even more exact compensation.
The operating voltage of the electrical machine frequently includes a common-mode voltage, which is a significant cause of bearing currents. It is thus advantageous to use the common-mode voltage as an input variable for the voltage production device. The bearing voltages are generally dependent on the common-mode voltage only via a motor-specific transformation ratio..
In one particular embodiment, the compensation apparatus according to the invention has a star circuit by means of which the phases of the electrical machine are connected at a star point, and in which the voltage at the star point is used as an input voltage for the voltage production device. This synthetically created star point means that there is no need to connect the windings of the machine at a star point, or for the star point to be accessible in the machine.
A three-phase electrical machine is preferably equipped with the compensation apparatus. In this case, as already mentioned, it is particularly advantageous for a star point to be provided in the machine and for it to be possible to tap off the voltage at the star point as an input voltage for the voltage production device. This means that there is no need for a synthetic star point for production of the compensation voltage.
The object mentioned above is also achieved by a compensation apparatus for prevention of damaging bearing currents having a first connection for connection to the rotor of an electrical machine, a second connection for connection to the housing or a potential of a voltage intermediate-circuit converter of the electrical machine, and an impedance with a low high-frequency reactance, which impedance is connected between the first and the second connection. An electrical machine according to the invention can be equipped with a compensation apparatus such as this. In this case, the idea is to ground the rotor via the compensation apparatus by only high frequencies. This makes it possible to avoid EDM bearing currents, that is to say the supply voltage for the motor is not used in this case.
The present invention will now be explained in more detail with reference to the attached drawings, in which:
The exemplary embodiments which are described in more detail in the following text represent preferred embodiments of the present invention.
The reason for the converter-dependent bearing currents is the so-called “common-mode voltage” in the pulse pattern of the voltage intermediate-circuit converter UR, which is illustrated in
Switching the electronic switching elements SE on and off leads to a change in the voltage across the parasitic capacitances in the motor, and thus to a current flow.
This motor design (see also
These electrical variables result in the single-phase equivalent circuit of a three-phase motor, as shown in
A change in the common-mode voltage Uo produces a current flow through the capacitance Cwh. This current results in a circular flow ZF in the motor windings MW which can lead to a damaging bearing current Ibearing, as is indicated in
The current Ie illustrated in
The lubricating film in the roller bearing can provide isolation only for a specific voltage, and then breaks down. A damaging bearing current can now be formed. The breakdown voltage is dependent on the lubricating film thickness and thus on the rotation speed, the temperature and the load on the bearing. The breakdown voltage is in the range 0.3 . . . 35 V. Bearing currents such as these have been described in the article by S. Chen, T. A. Lipo, D. Fitzgerald, “Modelling of bearing currents in inverter drives”, IEEE Transactions on Industry Applications, volume 32, pages 21-31, 1996.
According to the invention, the voltage across the roller bearings can be kept to values below the breakdown voltage by means of a suitable opposing voltage Uk. This prevents the described bearing current caused by the circular flow. A current caused by the circular flow now flows via the compensation apparatuses (
Damaging bearing currents may also be caused by discharge effects. In this case (see
The transformation ratio BVR is governed by the ratio of the voltage UZb across the bearing impedance Zb and the voltage UCwh across the capacitance Cwh . This ratio is typically between 0.02 and 0.2 .
A circuit KS1 or KS2 (see
The respective compensation device KS1 or KS2 is, in its simplest form, a pulse transformer or transformer T which applies the common-mode voltage Uo with an appropriate mathematical sign to the rotor RO as the opposing voltage, corresponding to the BVR of the motor. The common-mode voltage Uo reaches up to half the intermediate-circuit voltage Ud with conventional voltage intermediate-circuit converters. If, for example, the BVR is 5% and the common-mode voltage Uo is 300 V, the opposing voltage that must be produced is 15 V. The opposing voltage may be applied to the rotor RO via a sliding contact or via a capacitive coupling device.
The pulse transformer T is provided with circuitry networks ZT1, ZT2 in order to match the voltage form to the opposing voltage. This circuitry ZT1, ZT2 may, for example, be an RC combination and/or a varistor.
The pulse transformer T is fed via one or more coupling capacitors. If the common-mode voltage Uo is available at the star point SP (see
As shown in
The active circuit (AS) can also be designed such that the compensation apparatus KS3 provides a high-frequency ground for the rotor, irrespective of the common-mode voltage Uo.
A sliding contact is avoided, in order to connect the opposing voltage to the rotor reliably and without wear.
The bush BU and the isolating part IT may also, for example, be in the form of one component, which is mounted in the same way as a bearing.
No expensive current-isolating bearings or hybrid bearings for the prevention of damaging bearing currents are required when using the compensation apparatus KS1 to KS3 according to the invention. The life of the bearing is then advantageously increased, without the bearing currents, owing to the lack of groove formation or reduced grease aging.
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|1||Chen S., Lipot T., Fitzgerald D.: Modeling of Motor Bearing Currents in PWM Inverter Drives. In: IEEE Transactions on Industry Applications, vol. 32, No. 6, Nov./Dec. 1996, S. 1365-1370, 1996.|
|2||Chenggang Mei et al.: Minimization and cancellation of common-mode currents, shaft voltages and bearing currents for induction motor drives, vol. 4 of 4, Conf. 34, Jun. 15, 2003; pp. 1127-1132.|
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8878412 *||Apr 6, 2010||Nov 4, 2014||Ks Research S.A.||Alternating current electric induction motor with auxiliary closed loop toroidal winding|
|US9543812 *||May 1, 2014||Jan 10, 2017||Ge Energy Power Conversion Technology Limited||Multi-phase electric circuit|
|US9627945 *||Sep 27, 2013||Apr 18, 2017||Baker Hughes Incorporated||Systems and methods for preventing electrical arcing between components of an ESP motor|
|US20100253172 *||Apr 6, 2010||Oct 7, 2010||Ks Research S.A.||Alternating current electric induction motor|
|US20140327346 *||May 1, 2014||Nov 6, 2014||Ge Energy Power Conversion Technology Limited||Multi-phase electric circuit|
|US20150091399 *||Sep 27, 2013||Apr 2, 2015||Baker Hughes Incorporated||Systems and Methods for Preventing Electrical Arcing Between Components of an ESP Motor|
|U.S. Classification||318/632, 318/629, 327/551|
|International Classification||H02K11/00, H02K5/16|
|Cooperative Classification||H02K11/40, H02K11/20, H02K5/1732|
|European Classification||H02K11/00F, H02K11/00J|
|Oct 5, 2006||AS||Assignment|
Owner name: SIEMENS AKTIENGESELLSCHAFT, GERMANY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SCHREPFER, ARMIN;REEL/FRAME:018351/0340
Effective date: 20060726
|Oct 22, 2012||REMI||Maintenance fee reminder mailed|
|Mar 10, 2013||LAPS||Lapse for failure to pay maintenance fees|
|Apr 30, 2013||FP||Expired due to failure to pay maintenance fee|
Effective date: 20130310